enums seem to be ignored in certain cases

[sigmonsays]

in the service.proto file, https://github.com/sigmonsays/protoc-gen-gotemplate-examples/blob/master/src/ex1/service.proto we have Color defined as a enum type. It is not collected in the template, which can be seen here, https://github.com/sigmonsays/protoc-gen-gotemplate-examples/blob/master/src/ex1/templates/dump.txt.tmpl

The result of the template execution can be seen here https://github.com/sigmonsays/protoc-gen-gotemplate-examples/blob/master/src/ex1/dump.txt

It is my expectation that Color be in File.MessageType (and hence dump.txt) but it is not. Why is Color missed from being included in this scenario?